1. Field of the Invention
This invention relates to a bicycle caliper brake assembly, and more particularly to improvements in such a brake assembly which enables quick enlargement of an interval between a pair of brake shoes for ready wheel replacement.
2. Description of the Background Art
Most commonly used for bicycles is a side pull type caliper brake assembly which comprises a pair of calipers pivotally supported by a common support shaft and respectively retaining a pair of brake shoes in facing relation to both side walls of a bicycle wheel rim. The pair of calipers are always biased by a return spring so that the brake shoes are kept spaced from the wheel rim in a non-braking position. One of the calipers has a connecting portion connected to an outer cable of a double type control cable. The other of the calipers also has a connecting portion connected to an inner cable of the control cable which, when pulled up by a remote brake lever, causes the brake shoes to come into braking contact with the wheel rim against the biasing force of the return spring.
Generally, in such brake assembly, the brake shoes in their non-braking position are held as close to the wheel rim as possible in order to provide a quick response upon braking operation of the brake lever (hence a small play in braking). As a result, the interval between the brake shoes in their non-braking position is smaller than the width of a wheel tire (but larger than the width of the wheel rim). Thus, it is impossible to remove the wheel for replacement or repair.
One way to disassemble the wheel is to adjust the effective length of the inner cable or the outer cable by the use of screw means so that the interval between the brake shoes is temporarily enlarged enough for free passage of the wheel between the brake shoes. However, this measure requires a lot of time and is particularly disadvantageous in bicycle races or competitions where loss of time is vital.
In an attempt to meet the requirements for quick and ready wheel replacement, Japanese Utility Model Publication No. 56-15117 (Published: Apr. 9, 1981; application No. 53-93245; Filed: July 5, 1978; Applicant: Maeda Industries, Ltd; Inventors: Nobuo OZAKI et al) discloses a side pull type bicycle caliper brake assembly which has the same basic arrangement as described hereinbefore and additionally comprises a mechanism for quickly enlarging the interval between a pair of brake shoes in their non-braking position.
Such mechanism comprises a boss provided on a connecting portion of one caliper, a rotary member rotatably fitted in the boss and formed with an eccentric axial bore, and a cable retainer connected to an inner cable of a double type control cable and having a shaft inserted in the eccentric axial bore of the rotary member. The rotary member is also formed with an end flange facing one end face of the boss. The rotary member is rotated within a limited range by a pivotal adjusting lever connected thereto. The mechanism further includes a corrugated ring spring which urges the rotary member so that the end flange thereof comes into pressing contact with the one end face of the boss.
When the pivotal adjusting lever is in its lower limit position, the cable retainer is at a lower dead point with the pair of brake shoes spaced by a minimum interval. On the other hand, when the lever is pivoted to its upper limit position to bring the cable retainer to an upper dead point, the interval between the pair of brake shoes is increased to a maximum extent to allow free passage of a wheel between the pair of brake shoes for quick and ready replacement thereof.
The interval enlarging mechanism described above, however, has a disadvantage that the cable retainer cannot be held at a position intermediate the lower dead point and the upper dead point because a tensile force always applied to the inner cable acts to displace the cable retainer to the upper dead point due to the eccentricity of the cable retainer. Thus, it is impossible to use the interval enlarging mechanism also as a means for adjusting a play in braking operation.
The corrugated ring spring is intended to provide a frictional resistance between the rotary member and the boss which is sufficient to frictionally hold the cable retainer at any position between the lower dead point and the upper dead point against the tensile force acting on the inner cable. Contrary to such expectation, the actual frictional resistance imparted by the corrugated ring spring alone fails to serve the intended purpose.